Application of Crosta technique for porphyry copper alteration mapping, using ETM+ data: A case study of Meiduk and SAR Cheshmeh areas, Kerman, Iran
B ) Correlation matrix
| |
Band1 |
Band2 |
Band3 |
Band4 |
Band5 |
Band6 |
| Band1 |
1.000 |
0.944 |
0.892 |
0.732 |
0.666 |
0.711 |
| Band2 |
0.944 |
1.000 |
0.973 |
0.874 |
0.836 |
0.858 |
| Band3 |
0.892 |
0.973 |
1.000 |
0.921 |
0.874 |
0.896 |
| Band4 |
0.732 |
0.874 |
0.921 |
1.000 |
0.915 |
0.905 |
| Band5 |
0.666 |
0.836 |
0.874 |
0.915 |
1.000 |
0.980 |
| Band6 |
0.711 |
0.858 |
0.896 |
0.905 |
0.980 |
1.000 |
C ) Principal components for six bands
| |
PC1 |
PC2 |
PC3 |
PC4 |
PC5 |
PC6 |
|
| Band1 |
0.209 |
-0.540 |
-0.316 |
-0.348 |
-0.430 |
-0.509 |
| Band2 |
0.301 |
-0.408 |
-0.147 |
-0.297 |
0.068 |
0.793 |
| Band3 |
0.446 |
-0.437 |
0.121 |
0.508 |
0.535 |
-0.227 |
| Band4 |
0.359 |
0.002 |
0.844 |
-0.102 |
-0.384 |
0.017 |
| Band5 |
0.548 |
0.498 |
-0.121 |
-0.508 |
0.375 |
-0.197 |
| Band6 |
0.488 |
0.322 |
-0.370 |
0.515 |
-0.485 |
0.147 |
The principal component transformation (eigenvectors and eigenvalues) described in Table 1C , using six ETM+ bands as input bands( bands 1, 2, 3, 4, 5 and 6). As it is observed the first principal component does not contain spectral features relevant in this analysis as it is a combination of all bands with a major contribution from band -5. This component contains 91.2 per cent of the variance of six bands. This PC gives information mainly on albedo and topography. Vegetation is enhanced in PC3 as this PC has higher loading of band-4. PC4 enhances the hydroxyl minerals. This PC has higher loadings of bands 5 and 6 but with opposite signs. It has negative contribution of band 5 and positive contribution of band 6. Therefore pixels that map the hydroxyl minerals will be darker in the final hydroxyl image. But in order to show the areas with hydroxyl minerals in bright pixels an inverse of this PC is obtained(Figure 2). A similar analysis of PC5 shows that the most important contributions come from TM1(-0.43) and TM2(0.54). According to spectral characteristics of iron oxide(Hunt, 1978), it follows that iron oxide will be mapped by bright pixels(Figure 3). An average of hydroxyl and iron oxide images is also obtained. A false color composite image is made(hydroxyl image in red, iron oxide in green and average of these two in blue). In the resulted image all intensely hydrothermally altered areas are shown in bright pixels (Figure 4). The same technique is used on 4 bands. The only disadvantage with using this method on 4 bands is that the sedimentary rocks are also enhanced in the resulted image.